The invention relates generally to a multicylinder internal combustion engine with two exhaust turbosuperchargers and more particularly to an engine wherein one of the turbosuperchargers is selectively engageable under preselected engine operating conditions.
A supercharging system of an internal combustion engine having two exhaust turbosuperchargers has been disclosed in German DE-OS No. 28 18 447. The turbines are connected in parallel and their compressors are connected in series. Since the turbines and compressors of the two turbosuperchargers are of different dimensions, it is possible to operate only the smaller turbosupercharger under conditions of low exhaust output, thereby attaining effective turbosupercharging even in the lowest speed range of an internal combustion engine. With engagement of the larger turbosupercharger at higher exhaust output, there is lower pressure loss in the exhaust unit and the speed of the small turbosupercharger is reduced in the desired manner. One drawback of this system is the power break which occurs when the engine is reversed or the gears changed (which can occur suddenly and/or irregularly). The practicability of the vehicle provided with such an internal combustion engine can be reduced.
It is one object of the present invention to provide a turbosupercharging system which increases the torque and power of an internal combustion engine at lower speeds. It is another object of the present invention to provide a turbosupercharging system which is effective over the entire speed range of the engine without a noticeable power break.
These and other objects of the present invention are attained by the provision of a turbosupercharging system having two turbosuperchargers of the same type and dimensions, connected in parallel. A cut-in valve is installed in an exhaust manifold in which the turbine of the second turbosupercharger is installed. When the valve is closed, the entire exhaust blast coming from the engine is directed to the first turbine.
In this manner, even at low engine speeds, the first turbine can deliver an effective amount of power to its compressor, thereby introducing a detectable supercharge into the cylinders of the internal combustion engine.
This supercharge also holds a biased nonreturn valve which is built into the manifold pressure line of the second turbosupercharger in a closed position. When the cut-in valve is completely open, the exhaust blast is divided between the turbines of both superchargers, thereby allowing a pressure build-up until the biased nonreturn valve is suddenly opened and compressed air from both compressors is delivered to the cylinders. A specially adapted control system is provided for the nonreturn valve and a ventilation valve upstream of the nonreturn valve in order to prevent power loss or pulsations due to cutting in the second turbosupercharger.
Other objects and advantages of the present invention will be more apparent from the following detailed description of preferred embodiments, when taken in conjunction with the drawings.